1. Field of the Invention
This invention relates to improvements and obtaining a higher quality in methods of using urethane sand cores while facilitating the production process thereof. Also this invention relates to improving the manufacturing process and replacing gun-drilling operations through the casting thus improving cycle during the manufacturing process.
2. Description of the Prior Art for Casting
Hitherto a variety of fabrication methods have been employed for metal, plastic and ceramic. Casting as a part of machining has been extensively used to fabricate metal. Injection molding is extensively used to fabricate mold plastic or ceramic. In these fabrication processes of the above materials, a metal (non-disintegrative) core or a disintegrative core is generally used to fabricate articles having a hollow section and/or an undercut section.
The former metal core is used only in cases that the core can be directly extracted from a mold or extracted upon deformation of the fabricated article. Accordingly, used of the metal core is limited to a certain narrow range. The latter disintegrative core is usually formed of sand and therefore provided with the following disadvantages: The sand core is difficult to be formed to a predetermined shape and tends to easily disintegrate thereby rendering difficult handling thereof. Additionally, the sand core cannot meet conflicting requirements of compression resistance during fabrication and disintegration characteristics after the fabrication.
In this regard, it has been recently proposed in the field of casting of metal, to employ a sand core which is coated at its surface with a particular coating material so as to improve the compression resistance during casting. The coated sand core is used in a casting mold. However, even employment of such a coated sand core has the following difficulties:    (1) A plurality of layers of the coating material are required to be formed on the sand core, thereby making difficult formation of the coating layers. This troublesome operation increases the number of steps of a production process while increasing time and cost for the production process.    (2) It is difficult to completely remove binder as components of the coating material and the sand core, after casting. The removal of the binder is usually accomplished by burning or heat-treating the sand of the core. The burning step increases the number of steps of the production process while increasing time and cost for the production process.    (3) The sand core is difficult to be formed while requiring a complicated equipment and considerable steps in the production process. Additionally, the sand core tends to easily disintegrate and therefore is difficult in handling thereby increasing the number of steps in the production process while degrading the yield of the casting.    (4) During casting, a complicated pressure regulation is required to prevent the sand core from disintegrating. Additionally it is difficult to completely disintegrate the sand core after the casting. The above requires a heat-treatment step for the sand core and a sand removing step, and an inspection step for removal of sand from the resultant casting (product), which increases the number of steps in the production process thus increasing time and cost for the production process.    (5) Penetration of molten metal into among sand particles of the sand core and penetration of components of the sand core into the casting (product) are made during the casting. These tend to produce small holes or cavities in the casting thereby degrading the yield and productivity of the casting (product).    (6) Complete removal of sand of the sand core is difficult after the casting, so that the sand remains attached on the casting (product) thereby causing wear and damage of the casting (product).    (7) It is difficult or substantially impossible to produce a complicated and/or large casting. This limits the application of casting methods using the sand core to a narrow range, thus providing troubles in designing and production of castings.    (8) Reuse of sand of the sand core is difficult because the sand core contains the coating materials and the binder which are difficult to be completely removed. For reuse of the sand of the sand core, further steps are required in the production process thereby increasing time and cost for the production process.    (9) The casting method using the sand core and gun-drill is usually accomplished with the following steps which require increased production time and cost: (a) Forming a sand core; (b) Coating the sand core; (c) Drying the sand core; (d) Forming a casting mold; (e) Pouring a molten metal to accomplish a casting operation: (f) Removing sand from a casting (product); (g) Heat-treating the sand on the casting (product); (h) Inspecting completion of sand removing; (I) Removing burr from the casting (product); (j) sending casting product to machining line; (k) drilling manufacturing holes to zero the casting (product); (l) drilling the necessary hole(s) into the casting (product); (m) Obtaining a complete casting (product).It will be understood that the above-discussed problems in the casting method are encountered also in the molding methods (using the sand core) for casting iron and magnesium.
3. Description of the Prior Art for Replacing Gundrilling
Hitherto a variety of drilling methods have been employed for metal. Machining has been extensively used to fabricate metal. High speed machining tools in CNC Machines and standard carbide gundrills used in transfer line processes.
Regarding gun-drilling methods, a lot of money is needed in building a gun-drilling station and maintenance is needed in order to keep manufacturing processes going. Those methods are employed with the following difficulties:    (1) Coolant flow is difficult to regulate and causes gundrill breakage.    (2) Gundrills are used past their designated life and again gundrill breakage occurs.    (3) Stopping the line for changing the gundrill reduces cycle time in the manufacturing process.    (4) Maintenance and replacing parts of the gun-drilling station including the bushing, clamping, etc.